Architectural daylighting is the practice of placing windows http://en.wikipedia.org/wiki/Window or other openings and reflective surfaces so that, during the day, natural light provides effective internal lighting within a building structure. Particular attention is given to daylighting while designing a building when the aim is to maximize visual comfort or to reduce energy use, for example, from the reduced use of artificial (electric) lighting. One form of architectural daylighting involves utilizing a transparent or semitransparent sheet (e.g., glass) strategically mounted on a roof or vertical side wall of a building such that daylight is able to enter interior spaces of the building. In this way, sunlight is used to reduce our dependence on conventional (e.g., oil, coal and gas) energy sources.
Architectural daylighting arrangements are typically designed to deal with two types of daylight: diffuse (indirect) light and direct sunlight. Diffuse light is made up of non-parallel light beams originating from the sky hemisphere and possibly as scattered or reflected light from various physical objects in our environment. Diffuse light arrives at a give point with a low intensity (luminance) but since the angular zone of origin is large, it has a significant contribution to the light flux (e.g. −15% on a clear day). Diffuse light has particularly beneficial properties for daylighting. In contrast, direct sunlight is made up of approximately parallel light beams received directly from the sun, and has a relatively high intensity (luminance) in comparison to diffuse light. The ideal architectural daylighting arrangement attempts to maximize the amount of diffuse light allowed into a room/building while minimizing the amount of admitted direct sunlight in order to avoid undesirable high radiance areas, undesirable fluctuations of the lighting level, and/or excessive solar heating.
A problem with existing daylighting devices (e.g., clear, tinted or textured glass) is that these devices typically either allow too much direct sunlight or not enough diffuse light. Clear glass maximizes the amount of diffuse light transmitted into a room, but also allows too much direct sunlight during certain portions of the daylight hours. Tinted or textured glass serves to reduce the amount of direct sunlight, but typically at the cost of reducing the amount of diffuse light as well. The underlying disadvantage is that conventional systems have approximately similar transmission for direct and diffuse light.
What is needed is a solar light transmission apparatus that maximizes the amount of transmitted diffuse light, but minimizes the amount of transmitted direct sunlight. To achieve this, what is furthermore needed is a solar light transmission apparatus that in operation exhibits pronouncedly different transmission for direct and diffuse light, respectively.